DOC added link from banner to example.

The image in the banner from the front page now links to the example.

closes #2325
DBSCAN BallTree implementation
DOC now building to html/stable

closes #2314
DOC home always points to stable
Merge pull request #2329 from NelleV/website

DOC now building to html/stable
DOC credit to @ephes and myself for log loss in metrics
MISC: update whats_new
MISC: fix reference to example
DOC: DBSCAN misc doc formatting
DOC fix example comments

* @GaelVaroquaux's name was misspelled
* users won't know what a "Documentation merge" is
FIX: remove dupplicate entry in What's new

Actually, I was wrong - the Biclustering entry was the only dupplicate. Ping @GaelVaroquaux
ENH/FIX: improve logcosh function + tests
FIX/ENH: revert changes, improve doc
FIX: 80 characters
COSMITS
COSMITS
COSMITS
ENH: address discussion
ENH: use empty, not zeros
COSMITS